Modern consumer and industrial packaging often includes thermoplastically bonded tear tapes and reinforcing tapes as part of their constructions. Machines have been devised to apply these tapes in continuous fashion to packaging cartons conveyed adjacent one another on a conveyor. A much more difficult problem is posed if the packaging materials are placed at spaced intervals along the conveyor and if it is desired that only a short length of the tape be thermoplastically bonded to each. No satisfactory technique has heretofore been proposed to solve this problem.
Accordingly, there remains a need for a method and apparatus for applying short strips of tape to packaging materials that are conveyed in spaced relationship along a packaging line.
It is a principal object of the present invention to fulfill this need.
According to the present invention, an intermittent tape applicator is disclosed that consists of three major subassemblies: a tape dispensing subassembly, a tape strip transport subassembly and a thermobonding subassembly. The tape dispensing subassembly includes spindle-mounted tape spools for supplying thermoplastic tape to the applicator. The tension in the tape caused by unrolling from the spools is isolated from the remainder of the apparatus by a pair of nip rollers so as to improve consistency in length of tape cuts. From the nip rollers, the tape is routed through a cutting/feeding mechanism which determines the length of the tape strip. This mechanism is indexed to a predetermined application region on the articles (typically carton blanks) carried by a conveyor system.
The cutting/feeding mechanism consists of a rubber coated knife wheel, the circumference of which determines the cut length of tape. The tape strip is cut by a blade recessed below the rubber surface of the knife wheel that is exposed when the rubber portion of the wheel is depressed by engagement with a hardened anvil wheel. A leading edge of each tape strip cut thereby is pulled into an air flow amplifier unit, which is driven with low pressure compressed air so as to present a vacuum to the incoming tape strip. The tape is pulled by this vacuum into a transfer tube coupled to the air flow amplifier unit until its trailing end is cut by the next action of the knife blade against the anvil wheel. The tape then accelerates to the thermobonding subassembly at a rate controllable by air volume/pressure controls.
The thermobonding subassembly consists of a pair of endless thin steel bands mounted together so that the carton blank on the conveyor passes between them without slipping. The upper band is heated by a stationary hot shoe which heats the tape to its application temperature as it passes through the bands with the carton blank. The carton blank acts as a heat sink to help cool and solidify the tape after it leaves the thermobonding subassembly. A pressure point at the exit of the thermobonding subassembly provides a fixed and controllable nip which improves the uniformity of the tape application.